Our multifaceted investigation of normal and atypical melanocytes will be continued with major emphasis on the following topics: A. Characterization of the sites of hormonal and neural control in pigment cells through adenylate cyclase and phosphodiesterase activities and the relationship of these control sites to alpha and beta adrenergic receptors. B. Isolation of MSH-receptor molecules from malignant melanocytes. C. Isolation and analysis of mutant melanocytes defective in normal phenotypic expression. D. Examination of the viral-like structures in melanomas. E. Ultrastructural localization of tyrosinase, adenylate cyclase, and acetylcholinesterase in melanocytes. F. Study of the fine structure during transfer of melanin from melanocytes to keratinocytes.